This application claims the priority of German Application No.: 103 29 612.3 filed on Jun. 23, 2003, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a yarn withdrawal device for open-end spinning arrangements, comprising a yarn withdrawal nozzle, which contains a curved contact surface for guiding yarn which is to be withdrawn and which yarn simultaneously rotates in a crank-like manner, said contact surface graduating from a front surface into an axial channel, also comprising a balloon-breaking insert which extends the axial channel, the inner wall of the balloon-breaking insert being provided with raised areas/and or recesses with which the yarn comes into contact.
In open-end spinning, yarn withdrawal devices comprising yarn withdrawal nozzles in a great variety of embodiments are prior art. A plurality of such known yarn withdrawal nozzles, together with their advantages and disadvantages are described in German published patent application 197 38 382 (corresponding U.S. Pat. No. 6,035,625).
In the above mentioned publication it is disclosed that yarn withdrawal nozzles having smooth contact surfaces produce good quality yarn, but that yarn withdrawal nozzles of this type permit only a relatively low level of spinning stability, as the initial torsion upstream of the contact surface is too low due to the smoothness of the contact surface. Smooth yarn withdrawal nozzles are therefore particularly subject to end breaks.
The known publication describes further that so-called notch nozzles, that is, such yarn withdrawal nozzles whose contact surfaces are provided with notches or ribs increase the spinning stability, that is, they reduce the number of end breaks. This, however, is at the cost of the yarn quality, namely the tear resistance and the evenness of the spun yarn. Despite this, notched nozzles of this type have proven to be a good compromise and serve as the standard design in many applications.
It is further known from the publication that the notches can be present not only in the contact surface, but also in the annexing axial channel. This increases further the spinning stability, but at the cost of further reduced yarn quality. Notches and/or ribs in the axial channel ensure, however, a certain degree of hairiness of the spun yarn, which results in a “softer feel” which is often the intention.
The known publication further mentions that the so-called spiral nozzles are known in which the notches and/or ribs extend in the manner of a helix, and thus ensure a somewhat greater spinning stability than the smooth yarn withdrawal nozzles. The spinning stability is however less than in the case of such yarn withdrawal nozzles, in which the contact surface is notched. Spiral nozzles have, however, a relatively good yarn quality. The above mentioned publication further discloses that the spiral can project into the axial channel.
Also known from the above mentioned publication is a combination of notches and spirals, whereby serviceable yarn quality values with good spinning stability are assumed.
As the yarn withdrawal nozzles deflect the withdrawn yarn at approximately 90°, the yarn runs crank-like on the front surface of the yarn withdrawal nozzles at high speed. This results in that in the axial channel of the yarn withdrawal nozzle a certain balloon formation of the withdrawn yarn takes place. This has been taken advantage of in that so-called balloon-breaking inserts are arranged downstream, which are known in the industry as “whirl inserts”. A balloon-breaking insert of this kind is prior art in German published patent 32 20 402 (corresponding U.S. Pat. No. 4,516,397). This balloon-breaking inserts are especially then applied when it is intended that the spun yarn should have an increased hairiness. The surface structure of the spun yarn is changed by the balloon-breaking insert in that the yarn is roughened. This is basically fiber damage, so that the greater hairiness is gained with an inevitable reduction in tear resistance and evenness of the yarn. Such balloon-breaking inserts are basically spinning components which treat the yarns very roughly.
It is further known from German published patent 34 19 300 that the effect of such balloon-breaking inserts can be decreased by means of suitable ball-shaped inserts, whereby, depending on the design of the inserts, yarns with more or less hairiness can be spun. This publication discloses also that in addition the twist propagation, that is the spinning stability, can be influenced. The balloon-braking insert disclosed in this publication can be combined as required with yarn withdrawal nozzles having contact surfaces either with or without notches.
It is an aim of the present invention, based on the latter named publication, to pursue the further design of these undoubtedly correctly designed devices. One aim in particular is to spin yarn with a certain, but not too great, degree of hairiness, while at the same time, however, achieving good yarn values and good spinning stability.
This aim has been achieved in accordance with the present invention in that, in the case of a yarn withdrawal device of the above mentioned type, the contact surface of the yarn withdrawal nozzle is a smooth steel surface, and that the inner wall of the balloon-breaking device is provided with blunted raised areas/and or recesses reduced in such a way that a hairiness in the range of 3 mm in length can be achieved, while at the same time achieving values for spinning stability, wear resistance and evenness that are comparable to those resulting from notched contact surfaces of standard yarn withdrawal nozzles without balloon-breaking inserts.
The yarn withdrawal nozzle according to the present invention comprises firstly the advantage of a smooth contact surface, that is, without notches or ribs, which is responsible for a good yarn quality. A smooth contact surface of this type ensures yarn-friendly treatment of the withdrawn yarn in the particularly critical area. The steel surface permits sufficient hardness and thus wear-resistance of the contact surface, while at the same time ensuring a good carrying-off of heat, which is required in particular when spinning polyester fibers. The blunted balloon-breaking insert arranged downstream delivers the desired level of hairiness without too high a level of fiber damage. By means of simple tests, the right combination of a smooth yarn withdrawal nozzle with a suitable balloon-breaking insert can be found, whereby yarn quality and spinning stability values are achieved which are comparable to the notched yarn withdrawal nozzles without balloon-breaking inserts. The characteristics of the contact surface of a standard yarn withdrawal nozzle are thus transferred to a great extent to the balloon-breaking insert, which is present only for the purposes of achieving a certain pre-defined hairiness, while the contact surface of the yarn withdrawal nozzle itself is designed with regard to good yarn quality. The combination of a smooth yarn withdrawal nozzle comprising a contact surface of steel and having a reduced-effect balloon-breaking insert permits, by way of its flexibility, an even more specific adaptation of the yarn withdrawal device to the respective application than was previously possible.
It should be mentioned at this point that notched contact surfaces made of steel wear relatively quickly, as the notch forms are eroded so that spinning stability is no longer ensured after a short time. Contact surfaces of yarn withdrawal nozzles were therefore made of ceramic material as standard, which is less favorable with regard to heat elimination. In the case of the yarn withdrawal device of the present invention, it is in contrast now possible not only to make the contact surfaces from steel, but also to allocate the wear-prone part to the balloon-breaking insert, which part can then consist, at least on its inner wall, of a ceramic material.
In an embodiment of the present invention, a diameter contraction is provided between the axial channel of the yarn withdrawal nozzle and the balloon-breaking insert. The contraction causes the withdrawn yarn to be guided more in the center of the balloon-breaking insert so that the raised areas and/or recesses have a less aggressive effect. The contraction thus serves to blunt the effect of the balloon-breaking insert and can be achieved in a simple way in that the contracted part is placed in a separate intermediary ring. This has the additional advantage in that standard whirl inserts, which are actually aggressive, can be applied, the effects of which are blunted in the required way by means of this intermediary ring.
In a further embodiment of the present invention it can be provided that downstream of the balloon-breaking insert a centering device for permitting a centrical yarn withdrawal is provided. A centering device of this type also serves to blunt the effect of the raised areas and/or the recesses of the balloon-breaking insert. The centering device can in this case also be formed by means of a contraction, which in turn can be provided in a separate centering ring. The centering device can alternatively be formed by means of a yarn deflecting wall of a yarn withdrawal channel.
Many various embodiments can be chosen for the raised areas and/or recesses of the balloon-breaking insert. Ribs or notches can be provided which are arranged symmetrically or asymmetrically and if required, also helically, possibly extending in multiple helixes.
A particular advantage of the yarn withdrawal device of the present invention is then to be achieved when the yarn withdrawal nozzle and/or the balloon-breaking insert is designed as a replacement part. The most suitable yarn withdrawal device can be chosen and assembled for practically every desired yarn type.
These and further objects, features and advantages of the present invention will become more readily apparent from the following detailed description thereof when taken in conjunction with the accompanying drawings.